Weather resistant granules of various hues, embedded on the surface of asphalt impregnated base materials such as roofing felt have been used extensively to provide an aesthetically pleasing color to shingles. The color of the granules is usually attained by applying a coating containing pigment in a silicate/clay matrix to the mineral granules ground to a desirable particle size. The pigment employed for this purpose should have high weather resistant properties such as resistance to oxidation, UV exposure and wet/dry or freeze/thaw cycling. In addition, it is desirable that the pigment forms a firm bond with the silicate/clay matrix to achieve color stability.
In many areas, particularly in the north, dark hues such as black, rich brown and dark gray are preferred; while in other areas, as in the south, light colored roofing is desirable. In the later case, many of the lighter colors involve blending white or light color pigments with a darkening agent to provide a softer, more aesthetic appearance. However, many of the black or dark colored pigments do not possess high weatherability. Also, many pigments used in coatings lack high tint strength or resistance to high temperature firing called for in the coated mineral particle drying operation.
Accordingly, it is an object of this invention to provide a dark pigment for use in silicate/clay mineral coatings which overcomes the above disadvantages and which is suitable for coating mineral granules.
Another object is to provide a granule coating which possesses superior weatherability, good tint strength and color stability as well as heat stability.
Still another object of the invention is to provide a commercially feasible and economical process for the manufacture of the above granules.
Yet another object is to provide a superior granular coated roofing or siding shingle which is color stable and resistant to the deleterious effects of oxidation, UV light exposure and wet/dry or freeze/thaw cycling.
These and other objects of this invention will become apparent from the following description and disclosure.